The highly improved genome of with X and Y pseudochromosomes.

, the black-legged tick, is the principal vector of the Lyme disease spirochete, , and is responsible for most of the ∼470,000 estimated Lyme disease cases annually in the USA. can transmit six additional pathogens of human health significance. Because of its medical importance, was the first tick genome to be sequenced and annotated. However, the first assembly, Wikel (IscaW), was highly fragmented because of the technical challenges posed by the long, repetitive genome sequences characteristic of arthropod genomes and the lack of long-read sequencing techniques. Although has emerged as a model for tick research because of the availability of new tools such as embryo injection and CRISPR-Cas9-mediated gene editing yet the lack of chromosome-scale scaffolds has slowed progress in tick biology and the development of tools for their control. Here we combine diverse technologies to produce the Gulia-Nuss (IscGN) genome assembly and gene set. We used DNA from eggs and male and female adult ticks and took advantage of Hi-C, PacBio HiFi sequencing, and Illumina short-read sequencing technologies to produce a chromosome-level assembly. In this work, we present the predicted pseudochromosomes consisting of 13 autosomes and the sex pseudochromosomes: X and Y, and a markedly improved genome annotation compared with the existing assemblies and annotations.